the 1420 is the gpu clock which is the boost 2.0 and is automated. But every card has different limits due to the silicon lottery. My asic quality is 71%. I havent done a manual increase to the gpu clock, just the memory clock.
I have used DSR on a couple of games to play around with it but not on project cars.
DSR is just it renders at a higher resolution and then downscales.
DSR will be both memory heavy and gpu heavy as pixel count kills performance. In my view not a good idea on project cars.